1) Field Of The Invention
The present invention relates to a process for winding-up a film web onto a winding core to form a film reel, having a contact roll, via which the film web is fed to the film reel. The film reel and the contact roll rotate in opposite directions but at the same circumferential speed. Air boundary layers on the circumferential surface of the film reel and air boundary layers at the film web running over the contact roll are squeezed out before bringing together the two film webs. The present invention also relates to an apparatus for winding a film web.
2) Prior Art
Such a process and an apparatus for winding a film web are known from German Offenlegungsschrift 37 10 412 and operate, for example, satisfactorily for winding speeds up to about 100 m/min in the case of very thin film webs, for example 3 microns PET films.
In the production of films, the winding of the film web as the last process step has a considerable importance, since, in so doing, the film web meeting the specification may be wound "wrongly" to such an extent that a total loss of the film reel can occur due to damages to the film web, particularly during storage.
A particularly important problem in this context is represented by the phenomenon that considerable quantities of air can be enveloped in the film reel during winding. Some of this enveloped air escapes during the storing of the film reel and various defects, such as marks, stretches and cross waves, can occur in and on the film reel, which may cause the film reel to be completely unusable.
In the case of a known apparatus for winding sheet-like structures, the film web running onto the reel is pressed against the reel with the aid of a so-called contact roll, achieving the result that lesser quantities of air are enveloped during winding than without this measure. This apparatus is described in German Patent 32 65 570 (equivalent to U.S. Pat. No. 4,576,344). However, the air-displacing effect of the contact roll decreases with increasing winding speed, so that a compromise must be made between the winding speed and the enveloping of air. The entire phenomenology of air envelopment, with special consideration of the dependence of air envelopment on contact roll pressure against the reel, is the subject of research and development.
It has also been proposed to carry out the entire winding operation in a vacuum in order to solve the problem of air envelopment in this way, but the great financial expenditure is a factor against a realization of this proposal.
The object of the invention is to improve the process described at the beginning and to develop an apparatus for winding-up a film web in such a way that the winding speed can be increased substantially and that wind-up application for ultra-thin films with a thickness down to about 1 micron is possible.